Safety evaluation and protective effects of ethanolic extract from maca (Lepidium meyenii Walp.) against corticosterone and H2O2 induced neurotoxicity.

Maca has been traditionally used to enhance sexual behavior and fertility. Recently, maca's neuroprotective effects have been reported. The purpose of this study was to investigate whether the ethanol extract of maca (EEM) (100 mg/kg/bw, 200 mg/kg/bw, 400 mg/kg/bw, p.o.) exerted neuroprotective effects in corticosterone (CORT)-induced (40 mg/kg/bw, s.c.) rats, to determine the neuroprotective effects of EEM (12.5, 25, 50 µg/ml) and macamides in H2O2-induced (50 µM) PC12 cells. The acute toxicity (2000 mg/kg/bw, p.o.) and subacute toxicity (200 mg/kg/bw, 500 mg/kg/bw, 1000 mg/kg/bw, p.o.) of EEM were evaluated by mouse models. EEM reversed CORT-induced abnormal behaviors, reduced the contents of TNF-α, IL-6 in hippocampi, and increased the positive cells of doublecortin (DCX), bromodeoxyuridine (BrdU) and DCX + BrdU in the hippocampus of rats. Moreover, EEM and 4 macamides remarkably increased the cell viability in H2O2-induced PC12 cells. EEM promoted the phosphorylation of IκBα and p65, suppressed the NF-κB activation, and inhibited the levels of pro-inflammatory cytokines such as TNF-α, IL-6 and their mRNA levels in H2O2-induced PC12 cells. In conclusion, EEM could exert neuroprotective effects in CORT-induced rats and in H2O2-induced PC12 cells. Moreover, EEM did not present relevant toxicity after exposure to single and repeated doses.

Phenolic constituents with neuroprotective activities from Hypericum wightianum.

Five undescribed phenolic compounds, inclusing a depsidone derivative, hyperwightin A, a flavone derivative, hyperwightin B, and three benzophenone glycosides, hyperwightins C-E, along with four known ones were isolated from the 95% EtOH extract of the whole plants of Hypericum wightianum. Structures of the obtained compounds were elucidated by spectroscopic analyses. The protective effects of the isolates against corticosterone-induced PC12 cell injury were assessed. Hyperwightin E, petiolin G and hyperxanthone exhibited noticeable neuroprotection at 10 µM.

Dynamics of inflammatory reaction and oxidative stress across maternal serum, placenta and amniotic fluid in laboratory rats and the role played by genistein aglycone.

Background Genistein was reported to adversely influence fetal development although this is yet to be fully understood as a mechanism. Methods In this study, pregnant rats were divided into control (Cont.) and genistein force-fed (2-mg/kg and 4-mg/kg) groups. Each group was divided further into five subgroups: GD-0, GD-6, GD-13, GD-18, and GD-20 based on the terminal gestational day (GD). On the respective terminal GD, the rats were sacrificed and blood samples and amniotic fluid were carefully collected and separated and placenta homogenates were prepared. These samples were evaluated for oxidative stress and inflammatory reaction. The weights of embryonic implant and placenta tissue were also recorded. Heat shock protein (Hsp) (60 and 90), corticosterone, and oxidative stress biomarkers were determined in all the samples. Results Fetal and placental weights in all genistein-exposed groups were significantly decreased. A fluctuation in the level of the Hsp was recorded with a significant decrease recorded in Hsp90 level in the placenta and amniotic fluid towards GD-20 along with a concomitant increase in the corticosterone level in the amniotic fluid in all genistein groups compared to control. Maternal serum at GD-18 and GD -20 recorded a significant increase in antioxidant level (SOD, GSH, CAT) in all genistein-exposed groups. However, these antioxidants were significantly reduced in the placenta and the amniotic fluid compared to control. Conclusions Genistein enhances the placenta function in attenuating the risk of oxidative stress in the amniotic fluid and deferentially suppressed inflammatory activities in the placenta during early gestation and towards late gestation period.

Role of ibuprofen and lavender oil to alter the stress induced psychological disorders: A comparative study.

Stress has become an integral feature of everyday living. Each individual that lives encounters some manifestation of stress in life. Stress causes certain alterations in the structure and functions of the body and is considered to be a major factor in many health problems. Many synthetic and natural compounds are used for the attenuation of stress induced changes in the body. Medicinal plants are used since ancient times to prevent from neurological disorders. Lavender (Lavandula angustifolia) is very efficacious and possesses the ability to improve several neurological disorders. Nonsteroidal anti-inflammatory drugs (NSAIDs) are commonly used against pain and inflammation. However, effectiveness of NSAIDs in the treatment of various psychiatric ailments is also reported. The present study investigated the effects of ibuprofen and lavender oil on stress induced behavioral and biochemical alterations in rats. The rats were subjected to restraint stress and behavioral parameters like open field test (OFT), light/dark transition box activity (LDT) and forced swim test (FST) were used to assess exploratory, anxiolytic and anti-depressant activity, respectively. Corticosterone, lipid peroxidation (LPO) and endogenous antioxidant enzymes activities were also estimated. Results of OFT, LDT and FST showed substantial effects of lavender oil and standard drug ibuprofen. A significant decrease in plasma corticosterone and LPO levels with increase in antioxidant enzyme activities was observed in the study. However, the effects of lavender oil were more as compared to standard drug ibuprofen in diminution of stress induced behavioral and biochemical changes in rats. This study demonstrates that lavender oil is more remedial than ibuprofen in stress related disorders.

The role of 5-HT2c receptor on corticosterone-mediated food intake.

Corticosterone plays an important role in feeding behavior. However, its mechanism remains unclear. Therefore, the present study aimed to investigate the effect of corticosterone on feeding behavior. In this study, cumulative food intake was increased by acute corticosterone administration in a dose-dependent manner. Administration of the 5-HT2c receptor agonist m-chlorophenylpiperazin (mCPP) reversed the effect of corticosterone on food intake. The anorectic effects of mCPP were also blocked by the 5-HT2c receptor antagonist RS102221 in corticosterone-treated mice. Both corticosterone and mCPP increased c-Fos expression in hypothalamic nuclei, but not the nucleus of the solitary tract. RS102221 inhibited c-Fos expression induced by mCPP, but not corticosterone. In addition, mCPP had little effect on TH and POMC levels in the hypothalamus. Furthermore, mCPP antagonized decreasing effect of the leptin produced by corticosterone. Taken together, our findings suggest that 5-HT2c receptors and leptin may be involved in the effects of corticosterone-induced hyperphagia.

Mineralocorticoid receptor antagonist spironolactone prevents chronic corticosterone induced depression-like behavior.

High level of serum corticosteroid is frequently associated with depression, in which a notable HPA (hypothalamus-pituitary-adrenal) axis hyperactivity is often observed. There are two types of corticosteroid receptors expressed in the hippocampus that provide potent negative feedback regulation on the HPA axis but dysfunction during depression, i.e. the glucocorticoid receptor (GR) and the mineralocorticoid receptor (MR). The balance between hippocampal MR and GR during chronic stress plays an important role in the occurrence of depression. The aim of this study is to explore if chronic corticosterone administration would induce depression-like behavior and affect the expression and function of hippocampal MR and GR, in addition to assess whether manipulation of corticosteroid receptors would modulate depressive behaviors. Hence, mice were treated with corticosterone (40 mg/kg) for 21 days followed by assessment in a battery of depression-like behaviors. The results show that chronic corticosterone-treated animals displayed an increased immobility time in a forced-swimming test, decreased preference to sucrose solution and novel object recognition performance, and enhanced hippocampal serotonin but decreased MR expression in both hippocampus and hypothalamus. On the other hand, co-administration of MR antagonist, spironolactone (25mg/kg, i.p. × 7 days) in corticosteroid-treated animals reduced immobility time in a forced-swimming test and improved performance in a novel object recognition test. In conclusion, we demonstrate that chronic corticosterone treatment triggers several depression-like behaviors, and in parallel, down-regulates MR expression in the hippocampus and hypothalamus. Administration of an MR antagonist confers an anti-depressant effect in chronic corticosterone-treated animals.

Polysaccharides from wolfberry prevents corticosterone-induced inhibition of sexual behavior and increases neurogenesis.

Lycium barbarum, commonly known as wolfberry, has been used as a traditional Chinese medicine for the treatment of infertility and sexual dysfunction. However, there is still a scarcity of experimental evidence to support the pro-sexual effect of wolfberry. The aim of this study is to determine the effect of Lycium barbarum polysaccharides (LBP) on male sexual behavior of rats. Here we report that oral feeding of LBP for 21 days significantly improved the male copulatory performance including increase of copulatory efficiency, increase of ejaculation frequency and shortening of ejaculation latency. Furthermore, sexual inhibition caused by chronic corticosterone was prevented by LBP. Simultaneously, corticosterone suppressed neurogenesis in subventricular zone and hippocampus in adult rats, which could be reversed by LBP. The neurogenic effect of LBP was also shown in vitro. Significant correlation was found between neurogenesis and sexual performance, suggesting that the newborn neurons are associated with reproductive successfulness. Blocking neurogenesis in male rats abolished the pro-sexual effect of LBP. Taken together, these results demonstrate the pro-sexual effect of LBP on normal and sexually-inhibited rats, and LBP may modulate sexual behavior by regulating neurogenesis.

Curcumin reverses corticosterone-induced depressive-like behavior and decrease in brain BDNF levels in rats.

A rat model of depression has been recently developed using exogenous corticosterone (CORT) administration. This study aimed to examine the antidepressant-like effect and the possible mechanisms of curcumin in a CORT-induced depression model in rats. The results showed that 3-week CORT injections caused depression-like behavior in rats, as indicated by the significant decrease in sucrose consumption and increase in immobility time in the forced swim test. Repeated CORT injections also significantly decreased brain-derived neurotrophic factor (BDNF) protein levels in the hippocampus and frontal cortex of the rats. Treatment of the rats with curcumin significantly suppressed the depression-like behavior and the decrease in brain BDNF levels induced by the repeated CORT injections. The results suggest that curcumin produces an antidepressant-like effect in CORT-treated rats, which is possibly mediated by increasing BDNF expression in the hippocampus and frontal cortex.

Imipramine counteracts corticosterone-induced enhancement of glutamatergic transmission and impairment of long-term potentiation in the rat frontal cortex.

The effects of corticosterone administration lasting for 7 and 21 days were studied ex vivo in rat frontal cortex slices prepared 48 h after the last dose of the hormone. In slices originating from corticosterone-treated animals, the amplitude of extracellular field potentials recorded in cortical layer II/III was increased. Corticosterone administration also resulted in an increase of the mean frequency, but not the mean amplitude, of spontaneous excitatory postsynaptic currents (sEPSCs) in layer II/III pyramidal neurons. These effects were accompanied by a reduced magnitude of long-term potentiation (LTP) of field potentials. In a separate set of experiments, rats were treated with corticosterone for 21 days and additionally with a tricyclic antidepressant, imipramine, beginning on the eighth day of corticosterone administration. In this experimental group, the amplitude of field potentials, the mean frequency of sEPSCs and the magnitude of LTP were not different from the control, indicating that corticosterone-induced modifications of basal glutamatergic transmission and synaptic plasticity were reversed by the antidepressant.

NT-1, an active constituent extracted from Tiaoxin Recipe, enhances long-term potentiation of CA1 subfield in rat hippocampal slices.

Previous studies demonstrated that Tiaoxin Recipe (TXR), a traditional Chinese medicinal prescription, could alleviate cognitive dysfunction. NT-1, an active constituent isolated from this prescription under guidance of bioactive evaluation, was preliminarily proved to enhance the ability of spatial learning and memory in rats. In the present study, using hippocampal slice preparations, we investigated the mechanisms by which NT-1 improves cognitive dysfunction contributed to corticosterone (CORT). NT-1 ameliorated the inhibition of LTP by CORT more significantly than TXR did. These results suggested that enhancing LTP induction is one mechanism by which NT-1 improves spatial learning and memory impaired by CORT.

Choline exposure reduces potentiation of N-methyl-D-aspartate toxicity by corticosterone in the developing hippocampus.

Exposure to high levels of glucocorticoids (GCs) may adversely affect neuronal viability, particularly in the developing hippocampus, via increased function or sensitivity of N-methyl-D-aspartate (NMDA)-type glutamate receptors. Conversely, choline supplementation in the developing brain may reduce the severity of subsequent insult. The present studies aimed to examine the extent to which short-term exposure to high concentrations of corticosterone would produce neuronal injury mediated by NMDA receptor activity. These studies also assessed the ability of choline to prevent this form of injury via interactions with nicotinic acetylcholine receptors (nAChRs) expressing the alpha7 subunit. Organotypic hippocampal slice cultures derived from neonatal rat were pre-treated for 72 h with corticosterone (100 nM) alone or with choline (0.1-10 mM), prior to a brief (1 h) NMDA exposure (5 microM). NMDA exposure produced significant cellular damage, reflected as increased fluorescence of the non-vital marker propidium iodide, in the CA1 region. While exposure to corticosterone alone did not produce damage, pre-treatment of cultures with corticosterone markedly exacerbated NMDA-induced toxicity. Pre-treatment with choline (> or =1 mM) alone or in combination with corticosterone markedly reduced subsequent NMDA toxicity, effects blocked by co-exposure to methyllycaconitine (100 nM), an antagonist active at nAChRs expressing the alpha7 subunit. These data suggest that even short-term exposure to high concentrations of GCs may adversely affect neuronal viability and that choline supplementation protects the brain from NMDA receptor-mediated damage, including that associated with hypercortisolemia.

The cytoprotective effect of inulin-type hexasaccharide extracted from Morinda officinalis on PC12 cells against the lesion induced by corticosterone.

High concentration of corticosterone (Cort) 0.2 mM was incubated with PC12 cells to simulate the lesion state of brain neurons in depressive illness, it was found that the inulin-type oligosaccharides extracted from Morinda officinalis, inulin-type hexasaccharide (IHS) at the doses of 0.625, 1.25 microM or desipramine (DIM) 0.25, 1 microM protected the PC12 cells from the lesion induced by Cort. With Fura-2/AM labeling assay, DIM 0.25, 1 microM or IHS 2.5, 10 microM attenuated the intracellular Ca2+ overloading induced by Cort 0.1 mM for 48 h in PC12 cells. Using RT-PCR, treatment with Cort 0.1 mM for 48 h decreased the nerve growth factor (NGF) mRNA level in PC12 cells, IHS 5, 10 microM reversed this change. In summary, IHS attenuate the intracellular Ca2+ overloading and thereby up-regulate the NGF mRNA expression in Cort-treated PC12 cells, which may be consisted at least part of the cytopretective effect of IHS. These results also extend evidence for our hypothesis that neuroprotective action is one of the common mechanisms for antidepressants.

Hypoglycemic effect of Rehmannia glutinosa oligosaccharide in hyperglycemic and alloxan-induced diabetic rats and its mechanism.

The hypoglycemic and anti-diabetic effect of Rehmannia glutinosa oligosaccharide (ROS) in glucose-induced hyperglycemic and alloxan-induced diabetic rats and its mechanism was investigated in this paper. It was found that pretreatment of ROS in normal rats with 100 mg/kg for 3 days, i.p., induced a partial prevention of hyperglycemia caused by glucose (2g/kg, i.p.), while when hyperglycemia was induced in adrenalectomized (ADX) rats, the preventive effect of ROS on hyperglycemia was lost. In alloxan-induced diabetic rats, ROS (100 mg/kg for 15 days, i.p.) showed a significant decrease in blood glucose level and hepatic glucose-6-phosphatase activity with an increase in hepatic glycogen content. Furthermore, ROS raised plasma insulin level and lowered plasma corticosterone level in alloxan-induced diabetic rats. The results indicated that oligosaccharide of Rehmannia glutinosa Libosch. exerted a significant hypoglycemic effect in normal and alloxan-induced diabetic rats. The regulatory mechanism of ROS on glucose metabolism was adrenal dependent and had a close relation with the neuroendocrine system.

Sub-chronic treatment effects of an extract of Hypericum perforatum (St. John's Wort, Li 160) on neuroendocrine responses to the 5-T2A agonist, DOI in the rat.

Clinical studies have demonstrated the antidepressant efficacy of LI 160 extracts, which is comparable to antidepressants such as imipramine. The study was undertaken to assess the sub-chronic effects of LI 160 extract on plasma corticosterone and prolactin (PRL) responses to the post-synaptic 5-HT 2A receptor agonist, 2,5-dimethoxy-4-iodophenyl-2-aminopropane (DOI), in the male rat. Results show that sub-chronic treatment with the LI 160 extract reduced corticosterone and PRL responses to DOI. LI 160 may modify brain 5-HT function in the rat, possibly by reducing the sensitivity of central 5-HT 2A receptors. This may be a result of decreased receptor expression, signal transduction or intracellular messengers. These findings could be relevant to the therapeutic efficacy of St. John's Wort.

Inhibition of intracerebroventricular injection stress-induced plasma corticosterone levels by intracerebroventricularly administered compound K, a ginseng saponin metabolite, in mice.

Effects of major intestinal metabolites of ginsenosides, including compound K (IH-901, 20-O-beta-D-glucopyranosyl-20(S)-protopanaxadiol), compound Y (IH-902, 20-O-[alpha-L-arabinopyranosyl (1-->6)-beta-D-glucopyranosyl]-20(S)-protopanaxadiol), and ginsenoside Mc (IH-903, 20-O-[alpha-L-arabinofuranosyl (1-->6)-beta-D-glucopyranosyl]-20(S)-protopanaxadiol), on acute stress-induced plasma corticosterone levels were studied in mice. Intracerebroventricularly (i.c.v.) administered compound K (1 microg) attenuated the i.c.v. injection stress-induced increase in plasma corticosterone level, and this inhibitory effect was not affected by co-administered N(G)-nitro-L-arginine methyl ester, a nitric oxide synthase inhibitor. Compound K administered intraperitoneally affected neither the i.c.v. injection stress- nor the immobilization stress-induced increase in plasma corticosterone levels. Compound K and ginsenoside Mc did not affect plasma corticosterone levels induced by the two stress modalities used in this study.

[Antagonistic effect of aqueous extract of detoxified cottonseeds on corticosterone-induced lesion in cultured PC12 cells].

OBJECTIVE: To study the possible mechanism of aqueous extract of detoxified cottonseeds (CTN-W). METHOD AND RESULT: CTN-W 0.01, 0.03, 0.10, 0.30 mg.mL-1 was incubated directly with the synaptic membrane extracted from the cerebral cortex in rats, and adenylyl cyclase (AC) activity was detected by using radio-immunoassay. RESULT: Showed that CTN-W could activate AC in a dose-dependend manner. After incubation with PC12 cells in the presence of corticosterone 2 x 10(-4)mol.L-1 for 48 h, CTN-W 0.08, 0.4, 2 mg.mL-1 protected PC12 cells from the lesion induced by corticosterone. CONCLUSION: Antidepressant and anxiolytic effects of CTN-W are related with the activation of AC-cAMP pathway in signal transduction system, thus protecting neurons from the lesion. These two aspects maybe partly form the mechanism of CTN-W's action.

A high dose of vitamin E inhibits adrenal corticosterone synthesis in chickens treated with ACTH.

The present experiment was conducted to study the effects of dietary vitamin E on plasma corticosterone (CTC) concentration and adrenal steroid syntheses in chickens treated with adrenocorticotropic hormone (ACTH). Chickens were divided into ACTH(-) and ACTH(+) groups, and each group was further divided into three subgroups administered with vitamin E (500 or 5,000 mg/kg diet) and without the vitamin. Vitamin E (DL-alpha-tocopheryl acetate) was mixed with the basal diet at levels of 500 and 5,000 mg/kg and fed for 6 d. ACTH (20 IU/kg body weight) was given daily by intraperitoneal injection for 5 d. alpha-Tocopherol levels in the plasma and adrenal gland were markedly elevated by vitamin E feeding, and the level of adrenal free cholesterol (CHOL), which is used for steroid synthesis, was significantly decreased by vitamin E feeding in a dose-dependent manner. However, the level of adrenal CHOL ester was unchanged by any treatment. The elevations of pregnenolone, progesterone and CTC levels in the adrenal gland of chickens with ACTH treatment were decreased by vitamin E administration. The elevation of plasma CTC concentration in the ACTH(+) group was dramatically decreased by vitamin E administration, while that concentration was not influenced by the vitamin administration in the ACTH(-) group. These findings indicate that vitamin E suppresses the elevation of the plasma CTC concentration due to ACTH in chickens, possibly by inhibiting the conversion of CHOL ester to free CHOL in the adrenal gland.

Induction of obesity and hyperleptinemia by central glucocorticoid infusion in the rat.

It has been claimed that factors favoring the development or maintenance of animal or human obesity may include increases in glucocorticoid production or hyperresponsiveness of the hypothalamic-pituitary-adrenal axis. In normal rats, glucocorticoids have been shown to be necessary for chronic intracerebroventricular infusion of neuropeptide Y to produce obesity and related abnormalities. Conversely, glucocorticoids inhibited the body weight-lowering effect of leptin. Such dual action of glucocorticoids may occur within the central nervous system, since both neuropeptide Y and leptin act within the hypothalamus. The aim of this study was to determine the effects of glucocorticoids (dexamethasone) given intracerebroventricularly to normal rats on body weight homeostasis and hypothalamic levels of neuropeptide Y and corticotropin-releasing hormone. Continuous central glucocorticoid infusion for 3 days resulted in marked sustained increases in food intake and body weight relative to saline-infused controls. The infusion abolished endogenous corticosterone output and produced hyperinsulinemia, hypertriglyceridemia, and hyperleptinemia, three salient abnormalities of obesity syndromes. Central glucocorticoid infusion also produced a marked decrease in the expression of uncoupling protein (UCP)-1 and UCP-3 in brown adipose tissue and UCP-3 in muscle. Finally, chronic central glucocorticoid administration increased the hypothalamic levels of neuropeptide Y and decreased those of corticotropin-releasing hormone. When the same dose of glucocorticoids was administered peripherally, it resulted in decreases in food intake and body weight, in keeping with the decrease in hypothalamic neuropeptide Y levels. These results suggest that glucocorticoids induce an obesity syndrome in rodents by acting centrally and not peripherally.

Role of the hypothalamic pituitary adrenal axis and IL-6 in stress-induced reactivation of latent herpes simplex virus type 1.

Hyperthermic stress induces reactivation of herpes simplex virus type 1 (HSV-1) in latently infected mice and also stimulates corticosterone release from the adrenals via activation of the hypothalamic pituitary adrenal axis. In the present study, we tested the hypothesis that stress-induced elevation of corticosterone potentiates HSV-1 reactivation in latently infected mice. Because of the putative role of IL-6 in facilitating HSV-1 reactivation in mice, the effect of hyperthermic stress and cyanoketone treatment on IL-6 expression in the trigeminal ganglion was also measured. Preadministration of cyanoketone, a glucocorticoid synthesis inhibitor, blocked the stress-induced elevation of corticosterone in a dose-dependent manner. Furthermore, inhibition of corticosterone synthesis was correlated with reduced levels of HSV-1 reactivation in latently infected mice. Hyperthermic stress elicited a transient rise in IL-6 mRNA levels in the trigeminal ganglion, but not other cytokine transcripts investigated. In addition, there was a significant reduction in MAC-3+, CD8+, and DX5+ (NK cell marker) cells in the trigeminal ganglion of latent HSV-1-infected mice 24 h after stress. Cyanoketone blocked the stress-induced rise in IL-6 mRNA and protein expression in the trigeminal ganglion latently infected with HSV-1. Collectively, the results indicate that the activation of the hypothalamic pituitary adrenal axis plays an important role in stimulating IL-6 expression and HSV-1 reactivation in the trigeminal ganglion following hyperthermic stress of mice.

Effect of L-NAME, a specific nitric oxide synthase inhibitor, on corticotropin-releasing hormone-elicited ACTH and corticosterone secretion.

This study was designed to determine the role of endogenous nitric oxide (NO) in the corticotropin-releasing hormone (CRH)-induced ACTH and corticosterone secretion, as well as possible involvement of hypothalamic dopamine and noradrenaline in that secretion in conscious rats. CRH given i.p. stimulated dose-dependently the pituitary-adrenocortical activity measured 1 h later. Dexamethasone (0.2 mg/kg i.p.) injected 1 h before CRH (1 microg/kg i.p.) totally abolished the CRH-elicited ACTH and corticosterone secretion, indicating a predominantly pituitary site of CRH-evoked stimulation. L-arginine (120 mg/kg i.p.) and N(omega)-nitro-L-arginine methyl ester (L-NAME 5-10 mg/kg i.p.) did not markedly affect the basal plasma ACTH and corticosterone levels. L-NAME given 15 min before CRH markedly, but not significantly, augmented the CRH-induced ACTH response, and enhanced more potently and significantly the corticosterone response. Pretreatment with L-arginine, a substrate for NOS, slightly diminished the CRH-induced ACTH response and considerably reduced the corticosterone response. L-arginine also significantly reversed the L-NAME-evoked increase in the CRH-induced ACTH and corticosterone secretion. L-NAME did not markedly alter the CRH-induced hypothalamic dopamine and noradrenaline levels, while L-arginine significantly increased noradrenaline level. However, those alterations were not directly correlated with the observed changes in ACTH and corticosterone secretion. These results indicate that in conscious rats NO plays a marked inhibitory role in the CRH-induced ACTH secretion and inhibits more potently corticosterone secretion. Hypothalamic dopamine and noradrenaline do not seem to be directly involved in the observed alterations in ACTH and corticosterone secretion.